1、Section 5 DRILLED PILES AND SHAFTS 5.1 DESCRIPTION This work shall consist of constructing drilled foun- dation shafts, with or without bell footings, including the placing of reinforcing steel and concrete all in accor- dance with the plans, these specifications and the special provisions. 5.2 SUBM
2、ITTALS 5.2.1 Contractor Qualifications (Recommended where permitted by state law) (a) The Contractor shall have a minimum of 3 years experience in constructing shaft foundations of similar size, depth and site conditions within the past 5 years. Prior to shaft construction the Contractor shall submi
3、t written documentation of the three years experience to the Engineer for verification and acceptance. The sub- mittal shall include at least three projects on which the Contractor has previously been engaged in shaft con- struction with satisfactory results. A brief description of each project and
4、the owners contact persons name and current phone number shall be included for each project listed. (b) On-site supervisors shall have a minimum 2 years experience in construction of shaft foundations, and drill operators shall have a minimum 1 year experi- ence. Prior to the start of work, the Cont
5、ractor shall submit a list identifying the on-site supervisors and drill operators who will be assigned on the project. The list shall contain a summary of each individuals experience. (c) The Engineer will approve or reject the Contrac- tors qualifications and field personnel within 10 work- ing da
6、ys after receipt of the submission. Work shall not be started on any shaft until the Contractors qualifica- tions are approved by the Engineer. The Engineer may suspend the shaft construction if the Contractor substi- tutes unqualified personnel. The Contractor shall be fully liable for the addition
7、al costs resulting from the suspension of work, and no adjustments in contract time resulting from the suspension of work will be allowed . (d) A shaft preconstruction conference will be held with the Contractor and Sub-Contractor (if applicable) prior to the start of shaft construction to discuss c
8、onstruction and inspection procedures. This conference will be scheduled by the Engineer after the Contractors submittals are approved by the Engineer. 5.2.2 Working Drawings When required by the special provisions, at least four weeks before work on shafts is to begin, the Contractor shall submit t
9、o the Engineer for review and approval, an installation plan for the construction of drilled shafts. The submittal shall include the following: (a) List of proposed equipment to be used including cranes, drills, augers, bailing buckets, final cleaning equipment, desanding equipment, slurry pumps, sa
10、m- pling equipment, tremies or concrete pumps, casing (including: casing dimensions, material and splice de- tails), etc. (b) Details of overall construction operation sequence and the sequence of shaft construction in bents or groups. (c) Details of shaft excavation methods, and final shaft dimensi
11、ons. (d) When slurry is required, details of the method pro- posed to mix, circulate and desand slurry and disposal (e) Details of methods to clean the shaft excavation, including the bottom of the shaft. (f) Details of reinforcement placement including sup- port and centralization methods. (g) Deta
12、ils of concrete placement, curing and protec- tion, that demonstrates contractors ability to perform concrete placement in the required time. (h) Other information shown on the plans or requested by the Engineer. (i) Concrete mixes, and mitigation of possible slump loss during placement at the site.
13、 of slurry. 499 500 HIGHWAY BRIDGES 5.2.2 The Contractor shall not start the construction of drilled shafts for which Contractor qualifications and working drawings are required until such submittals have been approved by the Engineer. Such approval will not re- lieve the Contractor of responsibilit
14、y for results obtained by use of these submittals or any other responsibilities under the contract. 5.3 MATERIALS 5.3.1 Concrete Concrete shall conform to the requirements of Section 8. The concrete shall be Class A unless otherwise specified. NOTE: The concrete mix for drilled shafts shall be fluid
15、, consolidate under self-weight, be resistant to seg- regation, and have a set time that will assure that fluid- ity is maintained throughout the shaft concrete place- ment, and removal of temporary casing. The time for initial set of the shaft concrete should generally not ex- ceed 12 hours. 5.3.2
16、Reinforcing Steel Reinforcing steel shall conform to the requirements of Section 9, “Reinforcing Steel.” 5.3.3 Casings Casings which are required to be incorporated as part of the permanent work shall conform to the requirements of Section 11, “Steel Structures.” Steel shall be AASHTO M 183 (ASTM A
17、36), AASHTO M 270 (ASTM A 709) Grade 36, or ASTM A 252, Grade 2 or 3 unless otherwise specified. 5.4 CONSTRUCTION 5.4.1 Protection of Existing Structures All precautions shall be taken to prevent damage to ex- isting structures and utilities. These measures shall in- clude but are not limited to, se
18、lecting construction meth- ods and procedures that will prevent excessive caving of the shaft excavation, monitoring, and controlling the vi- brations from the driving of casing or sheeting, drilling of the shaft or from blasting, if permitted. 5.4.3 General Methods and Equipment Excavations require
19、d for shafts and bell footings shall be constructed to the dimensions and elevations shown on the plans. The methods and equipment used shall be suitable for the intended purpose and materials encoun- tered. Generally either the dry method, wet method, tem- porary casing method, or permanent casing
20、method will be used as necessary to produce sound, durable concrete foundation shafts free of defects. The permanent casing method shall be used only when required by the plans or authorized by the Engineer. When a particular method of construction is required on the plans, that method shall be used
21、. If no particular method is specified for use, the Contractor shall select and use the method, as determined by site conditions, subject to approval of the Engineer, that is needed to properly accomplish the work. The excavation shall be completed in a continuous operation. If the excavation operat
22、ion is stopped, the shaft cavity shall be protected by installation of a safety cover. It shall be the Contractors responsibility to en- sure the safety of the shaft excavation, surrounding soil and the stability of the side walls. A temporary casing, slurry or other methods approved by the Engineer
23、 shall be used if necessary to ensure such safety and stability. Excavations shall not be left open overnight unless cased full depth. The Contractor shall use appropriate means such as a cleanout bucket or air lift to clean the bottom of the excavation of all shafts. When unexpected obstructions ar
24、e encountered, the Contractor shall notify the Engineer promptly. The removal of such obstructions, and the construction of excavation shall be as directed by the Engineer. 5.4.4 Dry Construction Method The dry construction method shall be used only at sites where the groundwater table and site cond
25、itions are suit- able to permit construction of the shaft in a relatively dry excavation, and where the sides and bottom of the shaft remain stable without any caving, sloughing or swelling and may be visually inspected prior to placing the con- crete. The dry method consists of drilling the shaft e
26、xca- vation, removing accumulated water and loose material from the excavation, and placing the shaft concrete in a relatively dry excavation. 5.4.2 Construction Sequence 5.4.5 Wet Construction Method Where drilled shafts are to be installed in conjunction with embankment placement, they shall be co
27、nstructed after the placement of the fill and completion of any speci- fied settlement periods unless shown otherwise in the plans. The wet construction method shall be used at sites where a dry excavation cannot be maintained for place- ment of the shaft concrete. This method consists of using 5.4.
28、5 DIVISION II-CONSTRUCTION 501 water or mineral slurry to contain seepage, groundwater movement, and to maintain stability of the hole perimeter while advancing the excavation to final depth, placing the reinforcing cage and shaft concrete. This procedure may require desanding and cleaning the slurr
29、y; final cleaning of the excavation by means of a bailing bucket, air lift, submersible pump, cleanout bucket or other devices; and requires placing the shaft concrete with a tremie. Tempo- rary surface casings shall be provided to aid shaft align- ment and position, and to prevent sloughing of the
30、top of the shaft excavation, unless it is demonstrated to the sat- isfaction of the Engineer that the surface casing is not re- quired. Surface casing is defined as the amount of casing required from the ground surface to a point in the shaft ex- cavation where sloughing of the surrounding soil does
31、 not occur. 5.4.6 Temporary Casing Construction Method The temporary casing construction method shall be used at all sites where the stability of the excavated hole andior the effects of groundwater cannot be controlled by other means. Temporary casing may be installed by driving or vibra- tory proc
32、edures in advance of excavation to the lower limits of the caving material. Temporary casings shall be removed while the con- crete remains workable (i.e., a slump of 4 inches or greater). As the casing is being withdrawn, a 5 foot mini- mum head of fresh concrete in the casing shall be main- tained
33、 so that all the fluid trapped behind the casing is dis- placed upward without contaminating the shaft concrete. The required minimum concrete head may have to be in- creased to counteract groundwater head outside the cas- ing. Movement of the casing by rotating, exerting down- ward pressure and tap
34、ping to facilitate extraction or extraction with a vibratory hammer will be permitted. Casing extraction shall be at a slow, uniform rate with the pull in line with the shaft axis. 5.4.7 Permanent Casing Construction Method The permanent casing construction method shall be used only when required by
35、 the plans. This method gen- erally consists of driving or drilling a casing to a pre- scribed depth before excavation begins. If full penetration cannot be attained, the Contractor may either excavate material within the embedded portion of the casing or ex- cavate a pilot hole ahead of the casing
36、until the casing reaches the desired penetration. The pilot hole shall be no larger than one-half the diameter of the shaft and shall be centered in the shaft. Overreaming to the outside diame- ter of the casing shall not be performed unless specifically stated in the Plans or Special Provisions. Th
37、e casing shall be continuous between the elevations shown on the plans. Unless shown on the plans, the use of temporary casing in lieu of or in addition to the permanent casing shall not be used. After the installation of the casing and the excavation of the shaft is complete, the reinforcing steel
38、shall be placed, followed by the placement of the shaft concrete. After the permanent casing has been filled with concrete, any voids between the shaft excavation and the casing shall be pressure grouted with cement grout. The method of pressure grouting the voids shall be submitted to the Engineer
39、for approval. NOTE: Pressure grouting is required to assure contact (bearing) between the casing and any surrounding soil layer that is utilized for lateral support. 5.4.8 Alternative Construction Methods The Contractor may propose alternative methods to prevent caving and control ground water. Such
40、 proposals, accompanied by supporting technical data, shall be sub- mitted in accordance with Article 5.2, and are subject to the approval of the Engineer. 5.4.9 Excavations The bottom elevation of the drilled shaft shown on the plans may be adjusted during construction if the Engineer determines th
41、at the foundation material encountered dur- ing excavation is unsuitable or differs from that antici- pated in the design of the drilled shaft. When specified or shown in the plans, the Contractor shall take soil samples or rock cores to determine the char- acter of the material directly below the s
42、haft excavation. The Engineer will inspect the samples or cores and deter- mine the final depth of required shaft excavation. Excavated materials which are removed from the shaft excavation and any drilled fluids used shall be disposed of in accordance with the special provisions, and in compli- anc
43、e with federal and state laws. When bell footings are shown in the plans they shall be excavated to form a bearing area of the size and shape shown. 5.4.10 Casings Casings shall be metal, smooth, clean, watertight, and of ample strength to withstand both handling and driving stresses and the pressur
44、e of both concrete and the sur- rounding earth materials. The outside diameter of casing shall not be less than the specified diameter of the shaft. The inside diameter of the casing shall not be greater than the specified diameter of the shaft plus 6 inches unless otherwise approved by the Engineer
45、. Where the minimum 502 HIGHWAY BRIDGES 5.4.10 thickness of the casing is specified in the Plans, it is spec- ified to satisfy structural design requirements only. The Contractor shall increase the casing thickness as neces- sary to satisfy the casing strength requirements for han- dling and driving
46、 stresses. Temporary casings may be corrugated and nonwater- tight if conditions permit. 5.4.11 Slurry Slurry used in the drilling process shall be a mineral slurry. The slurry shall have both a mineral grain size that will remain in suspension and sufficient viscosity and gel characteristics to tra
47、nsport excavated material to a suitable screening system. The percentage and specific gravity of the material used to make the suspension shall be sufficient to maintain the stability of the excavation and to allow proper concrete placement. The level of the slurry shall be main- tained at a height
48、sufficient to prevent caving of the hole. The mineral slurry shall be premixed thoroughly with clean fresh water and adequate time allotted for hydration prior to introduction into the shaft excavation. Adequate slurry tanks will be required when specified. No excavated slurry pits will be allowed w
49、hen slurry tanks are required on the project without written permission of the Engineer. Ad- equate desanding equipment will be required when speci- fied. Steps shall be taken as necessary to prevent the slurry from “setting up” in the shaft excavation, such as, agitation, circulation, and adjusting the properties of the slurry. Control tests using suitable apparatus shall be carried out by the Contractor on the mineral slurry to determine density, viscosity, and pH. An acceptable range of values for those physical properties is shown in the following table: Range of Values (at 68F)
